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Notesclub

Histogram

8_histogram_reduce.livemd

Histogram

import IEx.Helpers

Build a histogram 3 ways

a. Build a histogram with library function

Example

histogram.build("apple")

apple

a | *
p | **
l | *
e | *
"lets get started on some elixir"
|> String.graphemes()
|> Enum.frequencies()
|> Enum.map(fn {key, value} ->
  "#{key} | #{String.duplicate(~s[*], value)}"
end)
|> Enum.join("\n")
|> IO.puts()
  | *****
a | *
d | *
e | *****
g | *
i | **
l | **
m | *
n | *
o | **
r | **
s | ***
t | ****
x | *
:ok

b. Histogram with Enum.map/1

"build a histogram with the map function"
|> String.graphemes()
|> Enum.group_by(fn x -> x end)
|> Enum.map(fn {k, v} ->
  {k, length(v)}
end)
|> Enum.map(fn {key, count} ->
  "#{key} | #{String.duplicate(~s[*], count)}"
end)
|> Enum.join("\n")
|> IO.puts()
  | ******
a | ***
b | *
c | *
d | *
e | *
f | *
g | *
h | ***
i | ****
l | *
m | **
n | **
o | **
p | *
r | *
s | *
t | ****
u | **
w | *
:ok

c. Histogram with Enum.reduce/3

# add one letter to frequency map

acc = %{"p" => 1, "a" => 1}
letter = "l"

# Map.put(acc, letter, acc[letter] + 1) broken because of non existent values

# Map.update(acc, letter, 1, &(&1 + 1))
add_one_letter =
  fn letter, acc ->
    Map.update(acc, letter, 1, fn x -> x + 1 end)
  end

# print one row
print_one_row =
  fn {letter, count}, acc ->
    stars = String.duplicate("*", count)
    row = "#{letter} | #{stars}"
    IO.puts(row)
    [row | acc]
  end

print_one_row.({"p", 2}, [])

# add one row to our output rows
"build a histogram with the map function"
|> String.graphemes()
|> Enum.reduce(%{}, add_one_letter)
|> Enum.sort()
|> Enum.reduce([], print_one_row)
p | **
  | ******
a | ***
b | *
c | *
d | *
e | *
f | *
g | *
h | ***
i | ****
l | *
m | **
n | **
o | **
p | *
r | *
s | *
t | ****
u | **
w | *
["w | *", "u | **", "t | ****", "s | *", "r | *", "p | *", "o | **", "n | **", "m | **", "l | *",
 "i | ****", "h | ***", "g | *", "f | *", "e | *", "d | *", "c | *", "b | *", "a | ***",
 "  | ******"]